BEHOLD! THE THREE EYED... SHRIMP?
About 250 million years ago, while dinosaurs roamed the Earth, evolution decided to try something else new. It decided to try a little crustacean with a distinctive shielded carapace, ringed tail ( not segmented as you might expect), and a primitive third “eye” between its stalkless but still shrimp-like compound eyes.
It lived in shallow, temporary pools and puddles, and gave up the filterfeeding lifestyle of its brachiopod relatives to become an omnivorous predator. This let the animal grow to an enormous size: up to 80 mm!
Truly, it was a perfect solution for a particular environment. How do we know? Because the shield shrimp has barely changed its form since. Australia’s single mainland species -
Triops australiensis - can be found in all those places that suffer cycles of drought and flood. Triops eggs need to desiccate, see, so they can blow on the wind and tumble their way to new dusty depressions in the bare earth.
When the rains come, and puddles form, Triops swarms. These crustaceans can reproduce sexually, or females can self-fertilise. Sometimes both in the one pond - that’s very unusual, but it’s also a great adaptation for living in Australia’s distinctive “low-energy” ecology. What if hardly any of the eggs in this pond are male? It doesn’t matter!
Triops of course means “three eyes”, although the third eye in this case is just a simple light-detector. It’s the kind of organ that several other crustacean species grow during their larval stage, only to discard after metamorphosis into the adult form.
But Triops has no larval stage. When eggs hatch, tiny little shield shrimp come out. They just get bigger, is all.
The ponds and puddles these creatures live in don’t last long. But that’s fine - a shield shrimp counts a 90 day life as a long, full life.
Want to check out these critters without a two-day car trip into the desert (and two year wait for rain)? Google “Billabong Bugs” to get a packet of eggs and enough food to last “generations”. They’re just like brine shrimp... except way way cooler.